Non-aqueous secondary batteries in which a non-aqueous electrolyte mediates electric conduction between electrodes include a lithium ion secondary battery. A lithium ion secondary battery is included in secondary batteries in which lithium ions contribute to electric conduction between electrodes in a charge/discharge reaction. Such a lithium ion secondary battery has characteristics of higher energy density and a smaller memory effect than other secondary batteries such as a nickel-hydrogen battery and a nickel-cadmium battery.
Hereby, application of the lithium ion secondary battery is growing to a variety of fields from a small size power supply used for portable electronics and electric home appliances up to middle and large size power supplies such as a stationary power supply used for power storage facility, an uninterruptible power supply system and a power leveling device, and a driving power supply used for a ship, a train, a hybrid train, a hybrid vehicle and an electric vehicle.
When the lithium ion secondary battery is used for middle and large size power supplies, especially demanded is highly improved energy density of battery. Realizing such highly improved energy density of battery needs a cathode and an anode both having highly improved energy density, and therefore demands an active substance having a highly improved capacity to be used for a cathode and an anode.
A cathode active substance having a high charge/discharge capacity is known as a powdery lithium composite compound represented by LiM1O2 (where M1 is an element such as Ni, Co and Mn or the like) having an α-NaFeO2 layered structure. This cathode active substance tends to show an increase in the capacity, especially as the nickel content is increased. Thus, a so called high-nickel cathode active substance having a high nickel content ratio is expected to be a promising candidate for realizing an improved energy density of battery.
A technology described in Patent Document 1 is known relevant to a high-nickel cathode active substance. A cathode active substance used for a lithium ion battery described in Patent Document 1 has a layered structure represented by the composition formula: Lix(NiyM1-y)Oz (where M is Mn or Co; 0.9≤x≤1.2; 0.6≤y≤0.9; and 1.8≤z≤2.4).
Herein, when an average secondary particle size of the powdery cathode active substance is represented by D50 and an average secondary particle size of the powdery cathode active substance thus pressed at 100 MPa is represented by D50P, a particle size ratio (D50P/D50) is 0.6 or more. Further, particles having a particle size of 0.4 μm or less with respect to the powdery cathode active substance thus pressed at 100 MPa are included at a volume ratio of 3% or less per entire particles.